LT5 Engine miss only in closed loop (hot) - ZR-1 Net Registry Forums

ZR1HOTC4 · 07-02-2006

Special thanks to TomTom72

for all the internet email quidance getting my beast roadworthy again. In a nutshell the car was missing pretty bad only in closed loop (when hot). When cold (open loop) the car ran fine. The scary part was the "noise" emitting from the dual mass flywheel trying to compensate for the miss at low rpms (idle). You'd think the rods were gone and I toasted the engine.

We chatted through the same issues TomTom72 experienced with the injectors, coils, etc... to diagnose the problem. After we were pretty much convinced the plenum had to come off and dive into the injectors, a buddy of mine (VW injection expert), was looking at the ZR1 engine and identifying all the similar parts and pieces to a VW - I'm not sure how he could see the similarities, but that's what makes him the expert. Well, eagle eyes like he has - he identified a gaping hole in the lower rubber PCV hose on the rear of the engine, drivers side. Sure enough - it was big enough to create a severe vacuume leak. My understanding is the PCV system doesn't engage until closed loop operation - hot engine. I put a glob (thats allot) of silicone sealant over the gaping crack (cleaned the oil residue off with alchohol first) and let it dry as a temporay repair to see if it made a difference. Later that day I took it for a test drive and the miss was pretty much gone, but it still wasn't running perfectly.

I ordered a new silicone hose from White racing and installed it last night - went in pretty slick and included a silicone top PCV vacuume manifold hose as well. Inspecting the old hose setup after removal, they had used a zip tie to hold the top manifold (vacuume) onto the tops of the two PCVs around the bottom hose which eventually collapsed the lower hose. The original top vacuume manifold had swollen from oil exposure so bad it was VERY loose on the PCV's - creating a secondary vacuume leak beyond the gaping crack in the lower hose. The new hose setup from White racing was so slick and tight fitting that there is absolutely no vacuume issues with the PCVs and the car runs a smooth as a kitten now. Not only that - now the cars alarm and the antenna goes down like it's suppose to? Do you think the car was trying to tell me something?

tomtom72 · 07-02-2006

Dave,

Great result!

I was glad to share whatever info I had with you. I was trying to share what the senior members shared with me when mine had troubles. We each try to help out when another member of the clan has trouble. I do truly believe that is what makes owning these cars special....the other owners!

Tom

Aurora40 · 07-02-2006

07-02-2006	#1
ZR1HOTC4 Join Date: Jun 2006 Location: Santa Maria, Ca Posts: 8	LT5 Engine miss only in closed loop (hot) Special thanks to TomTom72 for all the internet email quidance getting my beast roadworthy again. In a nutshell the car was missing pretty bad only in closed loop (when hot). When cold (open loop) the car ran fine. The scary part was the "noise" emitting from the dual mass flywheel trying to compensate for the miss at low rpms (idle). You'd think the rods were gone and I toasted the engine. We chatted through the same issues TomTom72 experienced with the injectors, coils, etc... to diagnose the problem. After we were pretty much convinced the plenum had to come off and dive into the injectors, a buddy of mine (VW injection expert), was looking at the ZR1 engine and identifying all the similar parts and pieces to a VW - I'm not sure how he could see the similarities, but that's what makes him the expert. Well, eagle eyes like he has - he identified a gaping hole in the lower rubber PCV hose on the rear of the engine, drivers side. Sure enough - it was big enough to create a severe vacuume leak. My understanding is the PCV system doesn't engage until closed loop operation - hot engine. I put a glob (thats allot) of silicone sealant over the gaping crack (cleaned the oil residue off with alchohol first) and let it dry as a temporay repair to see if it made a difference. Later that day I took it for a test drive and the miss was pretty much gone, but it still wasn't running perfectly. I ordered a new silicone hose from White racing and installed it last night - went in pretty slick and included a silicone top PCV vacuume manifold hose as well. Inspecting the old hose setup after removal, they had used a zip tie to hold the top manifold (vacuume) onto the tops of the two PCVs around the bottom hose which eventually collapsed the lower hose. The original top vacuume manifold had swollen from oil exposure so bad it was VERY loose on the PCV's - creating a secondary vacuume leak beyond the gaping crack in the lower hose. The new hose setup from White racing was so slick and tight fitting that there is absolutely no vacuume issues with the PCVs and the car runs a smooth as a kitten now. Not only that - now the cars alarm and the antenna goes down like it's suppose to? Do you think the car was trying to tell me something?

07-02-2006	#2
tomtom72 Join Date: Dec 2004 Location: Jacksonville, FL USA Posts: 4,645	Re: LT5 Engine miss only in closed loop (hot) Dave, Great result! I was glad to share whatever info I had with you. I was trying to share what the senior members shared with me when mine had troubles. We each try to help out when another member of the clan has trouble. I do truly believe that is what makes owning these cars special....the other owners! Tom __________________ 1990 ZR-1, Black/grey, #2233, stock. ZR-1 Net Reg Founding Member #316 & NCM member

07-02-2006	#3
Aurora40 Join Date: May 2005 Location: Leesburg, VA Posts: 2,713	Re: LT5 Engine miss only in closed loop (hot) __________________ Bob Saveland Former owner of #2517 [IMG]http://a.random-image.net/aurora40/vette.jpg[/img]